Tumor is one of the major diseases seriously threatening human life and affects the quality of life of the patients. According to the statistic data of World Health Organization (WHO), about 6.9 millions of patients die of tumors around the world each year. Due to the change of living environment and life habits, under the action of harmful environment and some adverse factors, morbidity and mortality of tumors have been increased in recent years.
Formerly, the treatment of tumors is done by finding and destroying the tumors. As the progress of researches in cell signal transduction pathways at present, the understanding of functions of oncogenes and anti-oncogenes in tumor cells is much comprehensive, it draws more attention to the design of new anti-tumor drugs aiming at tumor specific molecular targets. And targeted anti-tumor drugs as new therapies are applied in clinics, and have showen noticeable advances in recent years. It is reported protein tyrosine kinases (PTK) signaling pathway is closely related to the proliferation, differentiation, migration and apoptosis of tumor cells (Sun L., et al., Drug Discov Today, 2000, 5, 344-353), and the use of a protein tyrosine kinase inhibitor to interfere or block tyrosine kinase pathway has been applied to tumor treatment (Fabbro D., et al., Curr Opin Pharmacol, 2002, 2, 374-381).
Protein tyrosine kinase (PTK) is a member of the family of oncoproteins and proto-oncoproteins with important functions in normal and abnormal proliferation. This enzyme is capable of selectively phosphorylating tyrosine residue of different substrates, it catalyzes the γ-phosphate-group transfer of ATP to a tyrosine residue of many important proteins, so as to phosphorylate phenolic hydroxyl group. Protein tyrosine kinases are divided into receptor tyrosine kinases (RTK), non-receptor tyrosine kinases as well as IR and Janus kinases (Robinson D. R., et al., Oncogene, 2000, 19, 5548-5557), most of which are receptor tyrosine kinases (RTK). Receptor tyrosine kinases (RTK) are a group of endogenous protein tyrosine kinases, participate in the regulation of many cell activities, have important roles in transduction of mitogenicity signal in initiating cell replication, regulating the growth and differentiation of cells. All are type I membrane proteins, with similar topological structure. They all have one large glycosylated extracellular ligand binding domain, one hydrophobic single transmembrane domain, and one intracellular tyrosine kinase catalytic structural domain as well as regulatory sequence. It is the selevtive binding of ligand to receptor (such as the binding between epidermal growth factor (EGF) and EGFR) that results in the activation of partial coded receptor kinase in receipt cells, followed by the selective phosphorylation of tyrosine residue in target protein, then eventually leads to the transduction of proliferation signal through cytoplasmic membrane.
Most of cell growth factor receptors contain peptide sequence of tyrosine kinase, the overexpression or activation of different tyrosine kinases can be seen in many tumors, for example, EGFR overexpression is commonly seen in all of epithelial cell tumors; the overexpression of platelet-derived growth factor receptor (PDGFR) is commonly seen in glioma. According to the similarity of peptide sequences and structural features thereof, these receptors are further divided into several families: 1) epidermal growth factor receptor family, including EGFR, HER-2, HER-3, HER-4, etc. The overexpression of these receptors is commonly seen in epithelial cell tumors; 2) insulin receptor family, including insulin receptor, insulin-like growth factor receptor (IGF-R) and insulin relevant receptor (IRR), etc. The overexpression of these receptors is commonly seen in blood cancers; 3) platelet-derived growth factor receptor family (PDGFR), including PDGFR-α, PDGFR-β, CSF-1R, c-Kit, etc. The overexpression of these receptors is commonly seen in brain tumors, blood cancers; 4) fibroblast growth factor receptor (FGFR), including FGFR-1, FGFR-2, FGFR-3, FGFR-4, etc. These receptors play an important role in angiogenesis; 5) vascular endothelial cell growth factor receptor (VEGFR), including VEGFR-1, VEGFR-2, VEGFR-3, which are important positive regulatory factors for angiogenesis. The overexpression of tyrosine kinase receptor in different types of tumors results in abnormal activation of signals in cells thereof, leading to cell transformation, continuous proliferation, promoting generation and development of tumors, inhibiting cell apoptosis, so that targeting tyrosine kinase signaling pathway is a good strategy for developing anti-tumor drugs.
Vascular endothelial growth factor (VEGF) is a growth factor mainly acting on vascular endothelial cells. It has many functions such as promoting endothelial cell proliferation, increasing microvascular permeability, inducing angiogenesis (Hanks S. K., et al., FASEB, 1995, 9, 576-596). At present, known VEGF family includes 6 members: VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E and PDF. Wherein, VEGF-C is a new member of this VEGF family, which is obtained by separation and purification of human prostatic cancer cell line PC3 using Flt4 affinity chromatography (Joukov V., et al., EMBO J, 1996, 15, 290-298). VEGF-C can specifically activate Flt4 on lymphatic endothelium, so that VEGF-C is also called as lymphocyte growth factor. VEGF-C stimulates the growth of both vascular and lymphatic cells. The receptor of VEGF-C is VEGFR-2, which mainly distributed in vascular endothelial cells, promoting vascular endothelial cell proliferation, migration and vessel growth. The formation and development of tumors can be briefly divided into two stages: a stage of cloning proliferation of tumor cells, followed by a stage of angiopoiesis for promoting tumor continuous growth. VEGF acts on existing vascular endothelial cells and renders them differentiation to form new vessels. The new vessels not only provide a basis of substance exchange for tumor cells, but also enable paracrine secretion of some cell factors to promote the proliferation of tumor cells. And at the same time, due to the lack of integrity of vascular wall in newly generated vessels, endothelial cells are loosely linked between each other, basilar membrane has uneven thickness with breakage or absence, tumor cells may easily enter vessel cavity to result in invasion metastasis via blood flow. Hence, VEGF is closely related to tumor growth and metastasis. VEGF can be detected in many tissues of healthy human body, but its expression level is very low. On the contrary, it is overexpressed in many tumor tissues, especially in solid tumors, like liver cancer, brain cancer, breast cancer, lung cancer and kidney cancer (Samoto K., et al. Cancer Res, 1995, 55, 1189-1193; Ferrara N., Curr Opin Biotech, 2000, 11, 617-624; Shiladitya S., et al. Nature, 2005, 436: 568-572). Since the growth and metastasis of solid tumors depend on new vessels, VEGF is an ideal target for blocking solid tumor angiogenesis. There are two opinions in promoting tumor antiangiogenic researches, 1) health adults usually have relative less new vessels, and thus it is considered that antiangiogenic side effects are negligible; 2) the endothelial cells involve in angiogenic process are normal cells, and do not have unstable genome. This means antiangiogenic treatment would not result in drug-resistance. VEGFR is a diffusible vascular endothelium-specific mitogen and angiogenine receptor, which has critical function in physiological and pathological angiopoiesis processes, can inhibit the apoptosis of endothelial cells. This VEFGR family totally has 3 members, VEGFR1, VEGFR2, VEGFR3. At present, it is widely believed that angiopoiesis induced by VEGF is mediated by VEGF binding to VEGF receptor 2 (VEGFR-2) at vascular endothelial cell surface. After VEGF binds to VEGFR-2, VEGFR-2 forms a dimer which induces phosphorylation mediated by tyrosine kinase, and further activates relevant downstream signal transduction.
Platelet derived growth factors (PDGF) are mainly expressed in fibroblasts, smooth muscle cells, as well as kidney, testis and brain, and closely related to oncogenesis. In most of glioblastoma, there is an autocrine loop formed with PDGF and receptor thereof, including autocrine stimulation of PDGF in tumors. Overexpression or overactivation of PDGF receptor, and stimulating angiogenesis in tumors, all promote tumor growth.
In recent years, scientists are focused on the strategy of for inhibiting cell signal transduction pathway to develop new targeted anti-tumor drugs. Signal transduction inhibitor down-regulates the survival and proliferation signals of tumor cells, promotes cell apoptosis, not through cytotoxic effects. Therefore these types of therapy drugs have high selectivity and low toxicity. At present, a dozen of signal transduction inhibitors have been routinely used in clinic for treating tumors, mainly are tyrosine kinase inhibitor type anti-tumor drugs. Among them, multitarget indolone compounds are relatively well developed, examples including, the marketed multitarget tyrosine kinase inhibitor Sunitinib of Pfizer, the drug BIBF-1120 developed by Boehringer Ingelheim is now in phase III clinical trails, and other SU series of compounds (Abrams T J. Mol Cancer Ther., 2003, 2: 1011-21).
Sunitinib, tradename Sutent, is an indolone type small molecule multitarget RTKIs developed by Pfizer. It has inhibitory actions on many tyrosine kinase receptors, and can simultaneously inhibit targets such as VEGFR (−1, −2, −3), PDGFR-β, c-kit, FLT-3, to achieve anti-tumor effect by specifically blocking these signal transduction pathways. This drug show significant activity of inhibiting angiogenesis and against tumor cells. This drug was approved by FDA of the United State in January, 2006, and showed definite clinical efficacy, and it has obtained permission to be marketed in 61 countries including US, Europe, Japan, South Korea, indicated for gastrointestinal stromal tumor after disease progression on or intolerance to imatinib and advanced renal cell carcinoma.
In addition, WO 2008067756, WO 2008138184, WO 2008138232, WO 2007085188, WO 2005058309 and WO 2006002422 disclose pyrrolyl substituted dihydroindolone derivatives, having activity of inhibiting tyrosine kinases.
Small molecule tyrosine kinase inhibitors as new targeted anti-tumor drugs which open a new window for the treatment and prevention of tumors, and they have slight side effects and good tolerance. Although a dozen of small molecule tyrosine kinase inhibitors have brought great contribution for clinical treatment of tumors now, it is still need of discovering more compounds that have better in vivo activity and/or improved pharmacological properties in comparison with the existing tyrosine kinase inhibitors. Hence, it is still very important to develop new improved or highly effective tyrosine kinase inhibitors and to better understand the relationship between these drugs and known target proteins as well as their anti-tumor mechanisms.